This invention relates to a triarylimidazole derivative as an oxidizable color producing reagent, and a process for quantitatively determining an oxidizing substance or a peroxidase-like substance using said oxidizable color producing reagent.
Measurement of components in living body samples such as blood, urine, and the like has been essential for diagnosis of diseases, elucidation of diseases and judgement of the course of remedy, since changes of measured values greatly relate to diseases. Thus, there have been developed processes for measuring various kinds of trace amount components such as cholesterol, triglyceride, glucose, uric acid, phospholipids, bile acid, monoamine oxidase, etc. in blood. It is well known that these processes are very useful for diagnosis of diseases.
At present, as processes for measuring serum components, it is widely used in general so-called "enzymatic method" wherein an enzymatic reaction is carried out by either using an enzyme specifically act on an objective component when the objective component is other than enzyme, or using a compound as a substrate when the objective component is an enzyme, and measuring the product of the enzymatic reaction to obtain the amount of the objective component. Among these processes, there is increasingly used a process for measuring the amount of objective component comprising producing H.sub.2 O.sub.2 corresponding to the objective component by acting a hydrogen peroxide generating enzyme such as oxidase, leading the hydrogen peroxide to a color producing system using peroxidase and an oxidizable color producing reagent which is a color producing component, and measuring the color produced colorimetrically, with the development of oxidizable color producing reagents. For example, H.sub.2 O.sub.2 produced by a combination of cholesterol-cholesterol oxidase, triglyceridelipoprotein lipase-glycerol oxidase, uric acid-uricase, or the like is led to a color forming system by using peroxidase (POD) and an oxidizable color producing reagent, and absorbance of the color produced is measured to determine the amount of objective component. Typical examples of the oxidizable color reagent are a combination of 4-aminoantipyrine and a phenolic compound or an N,N-disubstituted aniline compound, a combination of 3-methyl-2-benzothiazolinonehydrazone (MBTH) and an aniline compound, 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid), triphenylmethane series leuco dyes, diphenylamine derivatives, benzidine derivatives, o-toluidine derivatives, o-phenylenediamines, etc.
But, almost all of these oxidizable color producing reagents except for the diphenylamine derivatives have color producing wavelengths of 600 nm or less and are easily influenced by serum components such as bilirubin, hemoglobin, etc. (easily influenced by coloring matters in urine in the case of measuring urine components). Further, there is another problem in that any chromogens except for the combined reagents with 4-aminoantipyrine and a part of triphenylmethane leuco dyes are low in stability.
On the other hand, as chromogens relatively good in stability and having a color producing wavelength at a relatively longer wavelength side, there have been disclosed triarylimidazole derivatives which are dye precursors (leuco dyes) (e.g. Japanese Patent Examined Publication Nos. 57-5519 and 57-26118, Japanese Patent Unexamined Publication Nos. 58-4557, 61-174267 and 61-227,570, U.S. Pat. No. 3,297,710, etc.). But even if these triarylimidazole derivatives are used as color producing component in the measurement of trace amount components in living body samples such as serum, urine, etc., no satisfactory results are obtained.